ED Sciences et environnements
Genetic and taxonomic diversity of isoetids communities in Aquitaine shallow lakes
by Estelle-Marie DEBAILLEUL (EABX - Écosystèmes aquatiques et changements globaux)
The defense will take place at 8h00 - Nouvel amphithéâtre EABX, INRAE, 50 avenue de Verdun, 33612 Cestas Cedex
in front of the jury composed of
- Aurélien JAMONEAU - Chargé de recherche - INRAE - Directeur de these
- Myriam VALERO - Directrice de recherche - Evolutionary Biology and Ecology of Algae (EBEA - CNRS) - Rapporteur
- Olivier LEPAIS - Directeur de recherche - INRAE - CoDirecteur de these
- Nicolas BECH - Maître de conférences - Université de Poitiers - Equipe Ecologie Evolution Symbiose - Rapporteur
- Guillaume EVANNO - Directeur de recherche - UMR DECOD, Rennes - Examinateur
- Gabrielle THIEBAUT - Professeure - ECOBIO CNRS, Rennes - Examinateur
This thesis examines correlations between genetic and taxonomic diversity (species-genetic diversity correlations, SGDC) within isoetid-dominated macrophyte communities in oligotrophic coastal lakes of Aquitaine. European priority habitat 3110, characterized by isoetids, is experiencing severe population declines of these protected species. The study focused on nine macrophyte species sampled across five lakes. Genetic analyses using microsatellite markers quantified genetic diversity via Hill numbers. SGDC correlations were examined through multiple approaches: variance decomposition, structural equation modeling, and NMDS ordination integrating genetic distance matrices (FST) and environmental variables. The first chapter establishes a genetic baseline for nine co-occurring species (two protected isoetids: Lobelia dortmanna and Littorella uniflora; seven more common species) across five lakes. Using microsatellite markers, the study reveals (1) a positive relationship between species rarity and genetic diversity; (2) remarkably high genetic differentiation (FST = 0.26-0.27), 3-10 times higher than typical aquatic plants, reflecting extreme fragmentation; (3) increasing clonality rates in degraded lakes as a response to environmental stress; and (4) consistent north-south genetic structure, revealing geographic isolation as the primary determinant. Subsequent chapters analyze SGDC correlations through multiple approaches: variance decomposition, structural equation modeling, and NMDS ordination integrating genetic distance matrices (FST) and environmental variables at both alpha and beta diversity levels. Only two species (B. ranunculoides and S. pungens) exhibit significant SGDC correlations, with environmental variables causally accounting for the observed correlations. Three distinct SGDC archetypes are identified; lake heterogeneity generates idiosyncratic local effects without systematic species-specific patterning. These findings demonstrate that genetic and taxonomic diversity do not automatically covary within isoetid communities. Conservation management of these Natura 2000 habitats must consider species-specific genetic dynamics and the critical importance of hydrological connectivity among fragmented lake systems to maintain adaptive potential of populations.